Biosurfactants are substances that have received a considerable amount of attention because of the fact that they possess a wide variety of interesting properties. For example, they can be used as oil recovery agents, emulsifiers, antibiotics and antifungal agents. In fact, Arima et al. have demonstrated in 1968 Biochem. Biophys. Res. Commun. 31:488-494 that a biosurfactant such as surfactin could reduce the surface tension of water from 72 to 27 mN/m at a concentration as low as 0.005% and could also inhibit clot formation. Furthermore, Bernheimer and Avigad in 1970 J. Gen. Microbiol. 61:361-369 have shown that surfactin could efficiently lyse erythrocytes while Hosono and Suzuki in 1983, J. Antibiot. 36:679-683 have demonstrated that bacterial spheroplasts and protoplasts as well as cyclic 3',5'-monophosphate diesterase could also be inhibited by the action of surfactin.
Biosurfactants are produced as metabolic products or membrane components. A considerable number of these compounds have been characterized and described by various authors such Cooper et al. (1986, Microbiol. Sci. 3:145-149), Cooper and Zajic (1980, Adv. Appl. Microbiol. 26:229-253), Margaritis et al. (1979, Biotech. Bioeng. 21:1151-1161), Rosenberg (1982, CRC Crit. Rev. Biotech. 1:109-132), Zajic and Steffens (1984, CRC Crit. Rev. Biotech. 1:87-107). These compounds are classified as lipopeptides, glycolipids, lipopolysaccharides, neutral lipids and fatty acids or phospholipids. They are surface-active due to their hydrophobic and hydrophilic regions. Since surfactants are used in many multiphase processes, they are very important industrially. Biosurfactants are potentially less toxic and more biodegradable than the synthetic compounds currently used. They can also be produced from a variety of substrates.
In particular, lipopeptides are a very interesting class of compounds. Some examples such as amphomycin (Bodanszky et al. 1973, J. Am. Chem. Soc. 95:2352-2357 and cyclosporin A (Dreyfuss et al., 1976, Eur. J. Appl. Microbiol. 3:125-133; Ruegger et al. 1976, Helv. Chim. Acta 59:1075-1092) are respectively known for their antibiotic and antifungal activities. They contain both a lipid portion and several amino acids.
Bacillus subtilis ATCC 21332 produces surfactin. Surfactin is a lipopeptide biosurfactant having as mentioned above quite interesting properties. Apart from being a very powerful biosurfactant, surfactin has the advantage of being easily isolated in pure form when produced by microorganisms such as B. subtilis. However, serious problems are associated with the industrial production of surfactin. Among these problems, the fact that the yields are very low is certainly the most important one.
Until now, the only methods which have been utilized to enhance production of surfactin by B. subtilis are strain selection or the manipulation of environmental or nutritional factor such as described in Cooper et al. in 1981, Appl. Environ. Microbiol. 42:408-412 and Guerra-Santos et al. in 1986 Appl. Microbiol. Biotech. 24:443-448. However, the methods that have been proposed so far are indirect methods having their limitations.
Therefore, the obtention of a B. subtilis strain able to produce large quantities of surfactin would be highly desirable.